How to change display format of POSIXct in R Console and RStudio View()

Question

I can read in dates from a CSV file to obtain a list of dates and times. My input looks like this:

2018/10/11 15:0:0

I read that into p1$hour. I need that in POSIXct, so I convert the string:

p1$timeUtc <- as.POSIXct(p1$hour,tz='Asia/Calcutta')

because the times in my CSV file are from India, IST timezone.

When I observe the attributes of p1$timeUtc, I see

attributes(p1$timeUtc)
$class
[1] "POSIXct" "POSIXt" 
$tzone
[1] "Asia/Calcutta"

If I ask for the value of an entry at the R console (within RStudio), I see

p1$timeUtc[[1]]
[1] "2018-10-11 15:00:00 IST"

The $tzone attribute is controlling the display format used. If I change it to UTC I see the same time displayed in a different zone:

> attr(p1$timeUtc,'tzone') <- 'UTC'
> p1$timeUtc[[1]]
[1] "2018-10-11 09:30:00 UTC"
> attr(p1$timeUtc,'tzone') <- 'Asia/Calcutta'
> p1$timeUtc[[1]]
[1] "2018-10-11 15:00:00 IST"

So I can affect the display format of the POSIXct variable without changing the value of the variable.

But if the csv datum happens to be midnight, 2018/10/12 00:0:0, the console output omits the time:

> p1$timeUtc[[2]]
[1] "2018-10-12 IST"

which is a little confusing. I'd just like it to be '%Y-%m-%d %H:%M %Z'.

Further, when I use View(p1) to display the data table in RStudio, that seems to use the tzone attribute, but omits the "IST" at the end. But it does print 2018-10-12 00:00:00 for midnight. (But maybe that's just because I am looking at a list, not one value?)

I know I can convert a POSIXct to a string and print that out however I want. But I don't want to do that; I want to specify how the R Console displays the POSIXct variable, and how the RStudio View() displays the variable. I can change the time zone used for display. Is there a way to change the format used for the rest? I looked in options for generic control but couldn't find a way.

Nathan Werth Nathan Werth · Accepted Answer · 2018-12-17T15:00:30

You can replace the print method for the class. Looking at the code for print.POSIXct:

function (x, tz = "", usetz = TRUE, ...) 
{
  max.print <- getOption("max.print", 9999L)
  FORM <- if (missing(tz)) 
    function(z) format(x, usetz = usetz)
  else function(z) format(x, tz = tz, usetz = usetz)
  if (max.print < length(x)) {
    print(FORM(x[seq_len(max.print)]), ...)
    cat(" [ reached getOption(\"max.print\") -- omitted", 
      length(x) - max.print, "entries ]\n")
  }
  else if (length(x)) 
    print(FORM(x), max = max.print, ...)
  else cat(class(x)[1L], "of length 0\n")
  invisible(x)
}

So the formatting is done with the FORM function created inside the method. You can make a new method with a couple edits to the code, and as long as it's named print.POSIXct, R will use it.

as.POSIXct("2018-12-17 00:00:00", tz = "UTC")
# [1] "2018-12-17 UTC"

print.POSIXct <- function (x, tz = "", usetz = TRUE, ...) 
{
  max.print <- getOption("max.print", 9999L)
  FORM <- if (missing(tz)) 
    function(z) format(x, usetz = usetz, format = "%Y-%m-%d %H:%M:%S")
  else function(z) format(x, tz = tz, usetz = usetz, format = "%Y-%m-%d %H:%M:%S")
  if (max.print < length(x)) {
    print(FORM(x[seq_len(max.print)]), ...)
    cat(" [ reached getOption(\"max.print\") -- omitted", 
      length(x) - max.print, "entries ]\n")
  }
  else if (length(x)) 
    print(FORM(x), max = max.print, ...)
  else cat(class(x)[1L], "of length 0\n")
  invisible(x)
}

as.POSIXct("2018-12-17 00:00:00", tz = "UTC")
# [1] "2018-12-17 00:00:00 UTC"

In general, you can overwrite any S3 class' methods by creating functions named like generic.class, where generic is the generic function's name and class is the class for which the method applies.

How to change display format of POSIXct in R Console and RStudio View()

1 Answers